Connected: An Internet Encyclopedia
RFC 822 - APPENDIX C. DIFFERENCES FROM RFC #733

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### APPENDIX C. DIFFERENCES FROM RFC #733

The following summarizes the differences between this standard and the one specified in Arpanet Request for Comments #733, "Standard for the Format of ARPA Network Text Messages". The differences are listed in the order of their occurrence in the current specification.

#### C.1. FIELD DEFINITIONS

#### C.1.1. FIELD NAMES

These now must be a sequence of printable characters. They may not contain any LWSP-chars.

#### C.2. LEXICAL TOKENS

#### C.2.1. SPECIALS

The characters period ("."), left-square bracket ("["), and right-square bracket ("]") have been added. For presentation purposes, and when passing a specification to a system that does not conform to this standard, periods are to be contiguous with their surrounding lexical tokens. No linear-white-space is permitted between them. The presence of one LWSP-char between other tokens is still directed.

#### C.2.2. ATOM

Atoms may not contain SPACE.

#### C.2.3. SPECIAL TEXT

ctext and qtext have had backslash ("\") added to the list of prohibited characters.

#### C.2.4. DOMAINS

The lexical tokens <domain-literal> and <dtext> have been added.

#### C.3. MESSAGE SPECIFICATION

#### C.3.1. TRACE

The "Return-path:" and "Received:" fields have been specified.

#### C.3.2. FROM

The "From" field must contain machine-usable addresses (addr-spec). Multiple addresses may be specified, but named-lists (groups) may not.

#### C.3.3. RESENT

The meta-construct of prefacing field names with the string "Resent-" has been added, to indicate that a message has been forwarded by an intermediate recipient.

#### C.3.4. DESTINATION

A message must contain at least one destination address field. "To" and "CC" are required to contain at least one address.

#### C.3.5. IN-REPLY-TO

The field-body is no longer a comma-separated list, although a sequence is still permitted.

#### C.3.6. REFERENCE

The field-body is no longer a comma-separated list, although a sequence is still permitted.

#### C.3.7. ENCRYPTED

A field has been specified that permits senders to indicate that the body of a message has been encrypted.

#### C.3.8. EXTENSION-FIELD

Extension fields are prohibited from beginning with the characters "X-".

#### C.4. DATE AND TIME SPECIFICATION

#### C.4.1. SIMPLIFICATION

Fewer optional forms are permitted and the list of three-letter time zones has been shortened.

#### C.5. ADDRESS SPECIFICATION

#### C.5.1. ADDRESS

The use of quoted-string, and the ":"-atom-":" construct, have been removed. An address now is either a single mailbox reference or is a named list of addresses. The latter indicates a group distribution.

#### C.5.2. GROUPS

Group lists are now required to to have a name. Group lists may not be nested.

#### C.5.3. MAILBOX

A mailbox specification may indicate a person's name, as before. Such a named list no longer may specify multiple mailboxes and may not be nested.

#### C.5.4. ROUTE ADDRESSING

Addresses now are taken to be absolute, global specifications, independent of transmission paths. The <route> construct has been provided, to permit explicit specification of transmission path. RFC #733's use of multiple at-signs ("@") was intended as a general syntax for indicating routing and/or hierarchical addressing. The current standard separates these specifications and only one at-sign is permitted.

#### C.5.5. AT-SIGN

The string " at " no longer is used as an address delimiter. Only at-sign ("@") serves the function.

#### C.5.6. DOMAINS

Hierarchical, logical name-domains have been added.

#### C.6. RESERVED ADDRESS

The local-part "Postmaster" has been reserved, so that users can be guaranteed at least one valid address at a site.

Next: APPENDIX D. ALPHABETICAL LISTING OF SYNTAX RULES

Connected: An Internet Encyclopedia
RFC 822 - APPENDIX C. DIFFERENCES FROM RFC #733